GN3 states that the purpose of IR test is to identify cable damage and short circuits. The latter it will but the former it will not, unless there is some kind of electrical continuity between the circuit conductors within the instrument range. The insulation could be stripped bare, gnawed by rodents or burned to a crisp and still the IR test could show an off-scale reading. 
The statement in GN3 could do with a cautionary note. 
Last week I witnessed two lads haul with all their might what looked like an oversized bundle of singles through several bends in steel conduit. My concern about damage was batted back with “sure it will be picked up in the IR test”!